This invention relates generally to the field of vehicular control, and in particular, to a method and system for progressive engagement of an all-wheel drive for a mobile vehicle.
All-wheel drive (AWD) systems use a center differential that allows the level of locking between the front and rear axles to be controlled. When the differential is totally unlocked, the vehicle stability in a turn may be maximized since the wheel speeds can be controlled by a Vehicle Stability Enhancement (VSE) subsystem without affecting the other axle. When the differential is totally locked, the traction of the vehicle is maximized since traction forces are supplied to all four wheels at a similar level. The optimal amount of locking should maintain a balance between the stability of the vehicle, the amount of all-wheel drive traction available, and driver comfort.
In order to achieve satisfactory vehicular performance under all road conditions, a control algorithm should provide variable engagement of AWD systems. When AWD systems are engaged without any estimates of surface capability, driver command, and vehicle state, instability of the vehicle may result or driver comfort may be negatively affected. Accordingly, it would be beneficial to have a system and method for using data from existing VSE subsystems such as yaw rate, lateral acceleration, and sensed wheel speed to provide these estimates, thereby engaging the AWD in a progressive manner to maintain stability and traction and to enhance the comfort of the vehicle user.
Furthermore, it would be beneficial to consider and incorporate the status of other vehicle subsystems, such as an anti-lock braking subsystem and a traction control subsystem, to produce smooth, progressive engagement and disengagement of an all-wheel drive system under varying road conditions and driver demands.
The object of this invention, therefore, is to provide a method and a system for progressive engagement of all-wheel drive, and to overcome the deficiencies and obstacles described above.
One aspect of the current invention provides a method of progressive engagement of all-wheel drive for a mobile vehicle. The method may include the steps of sensing a set of vehicle parameters, determining an all-wheel drive lock value based on the sensed set of vehicle parameters, determining vehicle subsystem control activation, adjusting the all-wheel drive lock value based on the vehicle subsystem control activation determination, and engaging an all-wheel drive controller based on the adjusted all-wheel drive lock value.
The sensed set of vehicle parameters may include lateral acceleration, steering wheel angle, yaw rate, and wheel speed. The all-wheel drive lock value may be based on a ratio of a sensed lateral acceleration and a surface capability value. The surface capability value may be computed from the sensed set of vehicle parameters.
The vehicle subsystem control activation determination may include determining whether a vehicle anti-lock brake subsystem is active, and adjusting the all-wheel drive lock value to an unlocked condition when the vehicle anti-lock brake subsystem is active. The vehicle subsystem control activation determination may include determining whether a vehicle traction control subsystem is active, and adjusting the all-wheel drive lock value based on a traction control subsystem gain value when the vehicle traction control subsystem is active. The traction control subsystem gain value may be a function of the surface capability value.
The vehicle subsystem control activation determination may include determining whether a vehicle stability enhancement subsystem is active, and adjusting the all-wheel drive lock value based on a stability enhancement subsystem gain value when the vehicle stability enhancement subsystem is active. The stability enhancement subsystem gain value may be a function of the surface capability value.
Adjustments to the all-wheel drive lock value may not be made when it is determined that the anti-lock brake subsystem is not active, the traction control subsystem is not active, and the vehicle stability enhancement subsystem is not active.
Another aspect of the current invention is a computer usable medium including a program for progressive engagement of an all-wheel drive. The computer program may include code to determine an all-wheel drive lock value based on the sensed set of vehicle parameters. The computer program may include code to determine vehicle subsystem control activation. The computer program may include code to adjust the all-wheel drive lock value based on the vehicle subsystem control activation determination. The computer program may include code to engage an all-wheel drive controller based on the adjusted all-wheel drive lock value.
The computer program may include program code to sense a set of vehicle parameters including lateral acceleration, steering wheel angle, yaw rate, and wheel speed. The computer program may include code to determine the all-wheel drive lock value based on a ratio of a sensed lateral acceleration and a surface capability value.
The computer program may include code to determine the surface capability value computed from the sensed set of vehicle parameters.
The computer program may include code to determine vehicle subsystem control activation that includes determining whether a vehicle anti-lock brake subsystem is active, and adjusting the all-wheel drive lock value to an unlocked condition when the vehicle anti-lock brake subsystem is active.
The computer program may include code to determine vehicle subsystem control activation that includes determining whether a vehicle traction control subsystem is active, and adjusting the all-wheel drive lock value based on a traction control subsystem gain value when the vehicle traction control subsystem is active. The computer program may further include code to determine the traction control subsystem gain value, which may be a function of the surface capability value.
The computer program may include code to determine vehicle subsystem control activation that comprises determining whether a vehicle stability enhancement subsystem is active, and adjusting the all-wheel drive lock value based on a stability enhancement subsystem gain value when the vehicle stability enhancement subsystem is active. The computer program may include code to determine the stability enhancement subsystem gain value, which may be a function of the surface capability value.
The computer program may include code to make no adjustment to the all-wheel drive lock value when it is determined that the anti-lock brake subsystem is not active, the traction control subsystem is not active, and the vehicle stability enhancement subsystem is not active.
Another embodiment of the current invention includes a system for progressive engagement of an all-wheel drive, including a means for sensing a set of vehicle parameters; a means for determining an all-wheel drive lock value based on the sensed set of vehicle parameters; a means for determining vehicle subsystem control activation; a means for adjusting the all-wheel drive lock value based on the vehicle subsystem control activation determination; and a means for engaging an all-wheel drive controller based on the adjusted all-wheel drive lock value.
The invention provides the foregoing and other features, and the advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention and do not limit the scope of the invention, which is defined by the appended claims and equivalents thereof.